[jira] [Commented] (FLINK-4241) Cryptic expression parser exceptions

["ASF GitHub Bot (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/FLINK-4241?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15510252#comment-15510252 ] 

ASF GitHub Bot commented on FLINK-4241:
---------------------------------------

GitHub user twalthr opened a pull request:

    https://github.com/apache/flink/pull/2529

    [FLINK-4241] [table] Cryptic expression parser exceptions

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    - [x] General
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    This PR improves the error message of the `ExpressionParser`. I tried my best but it is not easy to improve the message as we are using `RegexParsers`.

You can merge this pull request into a Git repository by running:

    $ git pull https://github.com/twalthr/flink FLINK-4241

Alternatively you can review and apply these changes as the patch at:

    https://github.com/apache/flink/pull/2529.patch

To close this pull request, make a commit to your master/trunk branch
with (at least) the following in the commit message:

    This closes #2529
    
----
commit 7d8d69f8b52983ccf078adfa2a78bf0855ec7cf9
Author: twalthr <tw...@apache.org>
Date:   2016-09-21T15:12:31Z

    [FLINK-4241] [table] Cryptic expression parser exceptions

----


> Cryptic expression parser exceptions
> ------------------------------------
>
>                 Key: FLINK-4241
>                 URL: https://issues.apache.org/jira/browse/FLINK-4241
>             Project: Flink
>          Issue Type: Improvement
>          Components: Table API & SQL
>    Affects Versions: 1.1.0
>            Reporter: Till Rohrmann
>            Assignee: Timo Walther
>
> The exceptions thrown when giving wrong SQL syntax to Flink's SQL parser is very cryptic and should be improved. For example, the following code snippet:
> {code}
> inputTable.filter("a == 0");
> {code}
> gives the following exception:
> {code}
> Exception in thread "main" org.apache.flink.api.table.ExpressionParserException: Could not parse expression: [1.4] failure: `-' expected but `=' found
> a == 0
>    ^
> 	at org.apache.flink.api.table.expressions.ExpressionParser$.parseExpression(ExpressionParser.scala:355)
> 	at org.apache.flink.api.table.Table.filter(table.scala:161)
> 	at com.dataartisans.streaming.SimpleTableAPIJob.main(SimpleTableAPIJob.java:32)
> 	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
> 	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
> 	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
> 	at java.lang.reflect.Method.invoke(Method.java:497)
> 	at com.intellij.rt.execution.application.AppMain.main(AppMain.java:144)
> {code}
> From this description it is very hard to understand that {{==}} is not a valid operator.
> Another example is:
> {code}
> inputTable.select("*");
> {code}
> which gives
> {code}
> Exception in thread "main" org.apache.flink.api.table.ExpressionParserException: Could not parse expression: Base Failure
> 	at org.apache.flink.api.table.expressions.ExpressionParser$.parseExpressionList(ExpressionParser.scala:342)
> 	at org.apache.flink.api.table.Table.select(table.scala:103)
> 	at com.dataartisans.streaming.SimpleTableAPIJob.main(SimpleTableAPIJob.java:33)
> 	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
> 	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
> 	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
> 	at java.lang.reflect.Method.invoke(Method.java:497)
> 	at com.intellij.rt.execution.application.AppMain.main(AppMain.java:144)
> {code}
> I think it would considerably improve user experience if we print more helpful parsing exceptions.



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